Bladder insert for encapsulant displacement

ABSTRACT

An encapsulated device and method for making such encapsulated device containing a bladder disposed between a wall of the case and the encapsulant. The bladder defines a space devoid of encapsulant and contains a collapsible insert such as an open cell foam material, thereby allowing the unimpeded thermal expansion of the encapsulant. By reducing thermal expansion stresses on the encapsulated devices, the reliability of the encapsulated device is improved.

This application is a continuation of Ser. No. 09/604,983 filed Jun. 28,2000, now U.S. Pat. No. 6,384,332 which is a continuation-in-part ofSer. No. 09/450,602 filed Nov. 30, 1999, now U.S. Pat. No. 6,303,860.

BACKGROUND OF THE INVENTION

This invention relates generally to the field of encapsulated componentsand to the manufacturing of such components. This invention relates morespecifically to the field of electrical components that are encapsulatedto improve their resistance to vibration and corrosive environments.

Encapsulation is a process by which a relatively fragile component issurrounded by an encasing material which provides mechanical support tothe component and which may seal the component from contact with theambient environment. Solid state electrical devices are known to besusceptible to printed circuit board failures due to vibration loadsand/or mechanical or electrical degradation caused by exposure to acorrosive environment. The assignee of the present invention providescomponents for the marine environment wherein high levels of vibrationand/or corrosive atmospheres may be commonplace. It is known toencapsulate such components to improve their performance in the marineenvironment. Encapsulants commonly used in such applications includeepoxy resin and urethane based products, and they are selected for theirworkability, mechanical strength and electrical insulating properties.As commonly practiced, the encapsulant is poured in a fluid state into acase containing electrical devices, then allowed to cure to form a solidmass encasing the electrical devices within the case.

While the known process is effective to protect a component againstvibration and environmental damage, failures may occur within thecomponent due to mechanical damage caused by the thermal growthcharacteristics of the encapsulant. For example, it is known that suchthermal growth may cause mechanical failure at the point where aconducting pin is soldered directly to a mating connector on a printedcircuit board when the pin is fully constrained by being molded into aplastic case. Encapsulant disposed between the printed circuit board andthe case is subject to thermal expansion and contraction. The thermalgrowth of the encapsulant may tend to move the printed circuit boardaway from the case. However, at the location of the soldered connection,the printed circuit board is maintained at a fixed distance from thecase. The thermal expansion of the encapsulant may impose unacceptablyhigh forces on the printed circuit board and/or the soldered connection.Encapsulated electrical components are known to have failed as theresult of such differential thermal expansion.

BRIEF SUMMARY OF THE INVENTION

Thus, there is a particular need for an improved method forencapsulating a component to avoid failures resulting from the thermalgrowth of the encapsulant. There is also a particular need for anencapsulated component having a greater resistance to thermal growthfailures.

Described herein is a method for encapsulating components within a case,the method comprising the steps of: forming a bladder having an interiorcontaining a collapsible insert; positioning the bladder within thecase; installing at least one component within a case; depositing anencapsulant in a fluid state within the case and allowing theencapsulant to transform to a solid state; and providing a ventconnection to the bladder interior so that the collapsible insert maycompress and expand as the solid encapsulant expands and contracts. Aproduct formed by such a process is also described herein, as well as akit to be used for encapsulating a component by the described process.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention will becomeapparent from the following detailed description of the invention whenread with the accompanying drawings in which:

FIG. 1 is a partial sectional view of a printed circuit board mountedwithin a case proximate an inflated bladder.

FIG. 2 is a partial sectional view of the apparatus of FIG. 1 afterbeing encased within an encapsulant.

FIG. 3 is a partial sectional view of the apparatus of FIG. 2 whereinthe bladder has been punctured by drilling a hole through the case.

FIG. 4 is a top view of the bladder of FIGS. 1-3.

FIG. 5 is a partial sectional view of a printed circuit board mountedwithin a case above a bladder containing a collapsible insert and havinga chimney portion extending above the level of the encapsulant forventing the interior of the bladder.

Similar or identical components illustrated on successive drawings areidentified with the same numeral in each drawing.

DETAILED DESCRIPTION OF THE INVENTION

The applicants have discovered a method and apparatus for accommodatingthe thermal growth of an encapsulant disposed within a case. In theembodiment illustrated in FIGS. 1-3 an electrical printed circuit boardis encapsulated within a case. The apparatus 10 includes a printedcircuit board 12 housed within a case 14. As is known in the art, case14 may be a one piece injection molded plastic component or a metalcomponent, a partial bottom wall of which is illustrated in FIG. 1. Aplurality of electrical devices 16 are mounted to printed circuit board12. The electrical devices 16 may constitute all or part of a circuit,such as for example, circuitry necessary to perform the function of apower supply. Electrical connection to the circuit board 12 is providedby one or more conductive pins 18. The pins 18 may be sealed within thewall of the case 14 as is known in the art of injection molding. Eachpin is illustrated as being soldered to a connector 20 mounted oncircuit board 12, thereby providing both mechanical and electricalconnections between the case 14 and the circuit board 12. Circuit board12 may also be supported mechanically by post 22 formed as an integralportion of the wall of case 14. A screw 24 is shown attaching thecircuit board 12 to post 22. The circuit board 12 may also be secureddirectly to the case 14 by a screw or clamp, or may be secured by theaction of a connector attached to the case.

A bladder 26 is positioned within the case 14, and may be attached to asurface of the case by an adhesive 28. Bladder 26 is a hollow structuredefined by a flexible wall member which takes a predetermined shape wheninflated to an internal pressure that is higher than the ambientexternal pressure. The bladder may be formed of a flexible, airtightmaterial, such as polyvinylchloride (PVC). Other materials ofconstruction for the bladder 26 may be selected for ease ofmanufacturing, electrical insulation properties, resistance to heat,and/or compatibility with the encapsulant material to be used. In theembodiment of FIG. 1, bladder 26 consists of two layers of PVC materialsealed on their respective edges 28 by a thermal sealing process.Bladder 26 is also illustrated as having a sealed hole 27 formed in onelocation for fitting around post 22. Such a hole 27 may be seen moreclearly in FIG. 4 which is a top view of bladder 26. FIG. 4 alsoillustrates the location of a section A—A which is the sectional view ofthe bladder 26 seen in FIGS. 1-3. Bladder 26 may be formed in anydesired shape, and it preferably will conform to the geometry of atleast a portion of the interior of case 14. The shape of bladder 26 isselected to match the shape of a desired space within case 14 devoid ofencapsulant, as will be described more fully below. The interior ofbladder 26 may be filled with air or other fluid so that the bladdertakes a predetermined shape when inflated. The bladder 26 may beinflated prior to being installed within the case 14, or for certainapplications, it may be installed in a deflated state and inflated onceit is in position within the case 14.

FIG. 2 illustrates the apparatus 10 of FIG. 1 after encapsulant 30 hasbeen deposited in the case 14. Prior to depositing the encapsulant 30,the printed circuit board 12, electrical devices 16 and case 14 may bepreheated to a predetermined elevated temperature, such as about 85degrees Centigrade, for a period of time sufficient to remove moisturefrom the components including the printed circuit board 12. Encapsulant30 in a fluid state is then poured into the case 14 to a predeterminedlevel. In certain embodiments, it may be necessary to tilt the case 14and enclosed components while introducing the encapsulant 30 in order toavoid the entrapment of air under the circuit board 12, thereby ensuringthe complete encapsulation of all of the devices 16. In the embodimentof FIGS. 1-3, bladder 26 is positioned so that it does not contact anyportion of the printed circuit board 12. This insures that theencapsulant 30 will fully encase the electrical devices 16 located onthe side of the circuit board 12 proximate the bladder 26. Encapsulant30 is allowed to cure to transform to a solid state with the bladder 26in its inflated condition, thereby forming a space devoid of encapsulant30 at a desired location within the case 14.

FIG. 3 illustrates the apparatus 10 of FIGS. 1-2 with a hole 32 havingbeen drilled through case 14, thereby causing a puncture 34 in bladder26. The puncture 34 allows the interior of bladder 26 to be in fluidcommunication with and at pressure equilibrium with the ambientenvironment of the apparatus 10. As encapsulant 30 grows due to anincrease in temperature, the space defined by the bladder 26 which isdevoid of encapsulant 30 may decrease to accommodate the thermalexpansion of the encapsulant 30. Without the puncture 34, thedeformation of encapsulant 30 and resulting decrease in volume of thespace devoid of encapsulant may result in an undesirable increase inpressure in bladder 26, thereby negating the desired affect of providingspace for the unimpeded thermal growth of encapsulant 30. Because theencapsulant 30 is free to grow into the space defined by bladder 26, thestresses generated in the printed circuit board and attached structuresare reduced. The material of bladder 26 is selected so that it remainsflexible during the operation of the apparatus 10 and so that it mayremain within the apparatus 10 throughout its operating life withoutdetrimental effect.

In lieu of drilling a hole 32 or otherwise penetrating the case 14 inorder to form puncture 34, the puncture 34 may be formed by cutting offa portion of bladder 6 extending above the top level of encapsulant 30.Alternatively, a valve may be attached to the wall of bladder 26 andmade accessible outside the area of the encapsulant 30. Once theencapsulant 30 has transformed to a solid state, the valve may be openedto provide a fluid communication path between the interior of thebladder 26 and the ambient environment.

The bladder 26 and encapsulant 30 may be supplied together with a fullyassembled apparatus 10, or they may be supplied separately as a kit forinstallation subsequent to the assembly of the circuit board 12 and case14. Such a kit may include a bladder 26 shaped to fit within the case14, along with a supply of encapsulant 30. The kit may also include asupply of adhesive 28, such as a tube of liquid adhesive, for securingthe bladder 26 in its proper position while the encapsulant 30 is pouredinto case 14.

FIG. 5 illustrates a cross-sectional view of an engine controller 40 fora marine propulsion apparatus wherein a bladder 26 is formed to containa collapsible insert 36. Circuit board 12 supports and interconnects aplurality of electrical devices 16 functional as part of a controlsystem for a marine engine (not shown). The type, quantity andinterconnection of such electrical devices 16 necessary to achieve suchfunctionality are well known in the art and may take any of manyembodiments. Bladder 26 is positioned within case 14 proximate thebottom 42 of the case 14 and may be affixed in its location by anadhesive 28. Bladder 26 is positioned between the circuit board 12 andthe case 14 to define a space devoid of encapsulant 30. In thisembodiment, there is no need to inflate bladder 26 since the collapsibleinsert 36 acts to maintain the bladder in an expanded condition duringthe pouring of the liquid encapsulant 30 into the case 14.

Flexible insert 36 may be a material having a resistance to crushingsufficient to support bladder 26 in an expanded condition during thepouring of encapsulant 30 against the bladder 26, and a compressibilitysufficient to allow for the expansion and contraction of encapsulant 30after it has hardened. In one embodiment, insert 36 is a section of2-pound open cell polyester foam, such as is provided by Federal FoamTechnologies, Inc. of New Richmond, Wis. The thickness of the insert 36may be selected as a function of the expected expansion and contractionof the encapsulant 30 over the expected temperature range, and as afunction of the allowable deflection in the circuit board 12 that may becaused by such expansion and contraction. In one embodiment a ¼ inchthick insert was used to create a space devoid of encapsulant thatotherwise would have been ¾ inch thick had it been completely filledwith encapsulant.

Bladder 26 is formed to have an opening 44, and an end of insert 36 mayextend therefrom. Opening 44 functions as a vent to allow air to flowout of and into the bladder 26 as the encapsulant 30 expands andcontracts during temperature changes. The opening 44 may be formed to bepart of a chimney portion 46 of the bladder 26. The chimney portion 46extends upward away from the bottom 36 of case 14 from a bend 48 to thevent opening 44 located above a top level 50 of encapsulant 30. Opening44 may be formed in the bladder 26 during its original construction byremoving a sealed edge portion of the chimney 46 or by not sealing aportion of the perimeter of the bladder 26. It is important that thecollapsible insert be free to expand the bladder 26 to an expandedcondition prior to the step of pouring the liquid encapsulant 30 intothe case 14. One method of manufacturing the bladder 26 is to sandwich alayer of open foam material between two layers of PVC material and tosonically seal weld the edges of the PVC material together. The edges ofthe foam material are spaced away from the edges of the PVC material tobe welded in order to ensure that a good seal is created. The bladdermay be pressed flat during the welding process to improve the qualitycontrol of the welding process. Unless there is a path for air to enterthe bladder after the welding process, the two layers of PVC materialwill remain in a collapsed state. In this case, it is important for thevent opening 44 to be formed prior to the step of pouring the liquidencapsulant 30 into the case 14 in order to ensure that the collapsibleinsert 26 can expand the bladder 26. Preferably, insert 36 extendsthrough bend 48 to prevent the bladder sides from collapsing andcreating a seal preventing the flow of air into and out of the interiorof the bladder 26. This is particularly important when the bladder willbe exposed to an elevated temperature in order to remove moisture beforethe encapsulation process, since the elevated temperature may act tocause a welding of the opposed sides of the bladder within the bend 48.

It is possible to use the embodiment of FIG. 5 without a separatebladder material and with only the collapsible insert 36 defining thespace devoid of encapsulant. The selection of materials for such anapplication must consider any possible flow of the encapsulant 30 intothe collapsible insert 36 prior to the hardening of the encapsulant 30.For example, if an open cell foam material is used for the insert 36,the size and material of the cells and the viscosity of the liquidencapsulant will determine the rate of flow of the encapsulant into thecells. Any such migration of encapsulant prior to its solidificationwould, of course, decrease the compressibility of the insert 36 andshould be accounted for in the selection of the thickness of the insert.It is also possible to cover the insert 36 with a barrier material thatis impervious to the liquid encapsulant to prevent this undesirablemigration of encapsulant into the insert 26. Such barrier materials mayinclude, for example, a PVC plastic or a common kitchen cooking wrap.One or both sides of the insert 36 may need to be covered, dependingupon the specific application. Federal Foam Technologies, Inc. of NewRichmond, Wis. provides an open cell foam product laminated with aflexible polyester film that may be useful in such applications.

While the preferred embodiments of the present invention have been shownand described herein, such embodiments are provided by way of exampleonly. Numerous variations, changes and substitutions will occur to thoseof skill in the art without departing from the invention herein. Forexample, the embodiment illustrated in FIGS. 1-3 is for an electricalprinted circuit board component. Other embodiments may include, forexample, discreet electrical components, mechanical devices, sensors, orfragile containers, etc. mounted in a case. Accordingly, it is intendedthat the invention be limited only by the spirit and scope of theappended claims.

I claim:
 1. A method of encapsulating components within a case, themethod comprising the steps of: forming a bladder having an interiorcontaining a collapsible insert; positioning the bladder within a case;installing at least one component within the case; and depositing anencapsulant in a fluid state within the case and allowing theencapsulant to transform to a solid state with the bladder forming aspace devoid of Encapsulant.
 2. The method of claim 1, wherein the stepof positioning further comprises attaching the bladder to a surface ofthe case.
 3. The method of claim 1, wherein the step of positioningfurther comprises positioning the bladder not to contact any portion ofthe at least one component.
 4. The method of claim 1, furthercomprising: attaching the bladder to a bottom surface of the case;mounting a circuit board in the case above the bladder; and tilting thecase while pouring the encapsulant into the case to ensure that theencapsulant flows between the bladder and the circuit board.
 5. Themethod of claim 1, further comprising the steps of forming the bladderto have the space form a fixed shape and positioning the bladder in apredetermined location within the case so that a space devoid ofencapsulant created by the bladder has a predetermined shape andlocation relative to the case and the at least one component.
 6. Themethod of claim 1, further comprising the steps of heating the at leastone component, bladder and case to remove moisture prior to the step ofdepositing an encapsulant.
 7. The method of claim 1, wherein the step offorming a bladder having an interior containing a collapsible insertcomprises the steps of: providing an open cell foam material; providinga layer of plastic material on each of opposed sides of the open cellfoam material; and sealing respective mating edges of the plasticmaterial around a perimeter of the open cell foam material.
 8. Themethod of claim 7, wherein the step of providing a vent connectioncomprises removing a portion of the sealed mating edges.
 9. A product bythe process of: forming a bladder having an interior containing aninsert; positioning the bladder within a case; installing at least onecomponent within the case; and depositing an encapsulant in a fluidstate within the case and allowing the encapsulant to transform to asolid state with the bladder forming a space devoid of encapsulant. 10.The product of claim 9, formed by the further step of attaching thebladder to a surface of the case.
 11. The product of claim 9, formed bythe further step of positioning the bladder not to contact any portionof the at least one component.
 12. The product of claim 9, formed by thefurther steps of: attaching the bladder to a bottom surface of the case;mounting a circuit board in the case above the bladder; tilting the casewhile pouring the encapsulant into the case to ensure that theencapsulant flows between the bladder and the circuit board.
 13. Theproduct of claim 9, formed by the further steps of forming the bladderto have the space have a fixed shape and positioning the bladder in apredetermined location within the case so that a space devoid ofencapsulant created by the bladder has a predetermined shape andlocation relative to the case and the at least one component.
 14. Theproduct of claim 9, formed by the further steps of heating the at leastone component, bladder and case to remove moisture prior to the step ofdepositing an encapsulant.
 15. The product of claim 9, wherein the stepof forming a bladder having an interior containing a collapsible insertcomprises the steps of: providing an open cell foam material; providinga layer of plastic material on each of opposed sides of the open cellfoam material; and sealing respective mating edges of the plasticmaterial around a perimeter of the open cell foam material.
 16. Theproduct of claim 15, formed by the further step of removing a portion ofthe sealed mating edges to provide a vent connection.
 17. An apparatuscomprising: a case; an electrical component disposed within the case;encapsulate disposed within the case and in contact with at least onesurface of the electrical component; a bladder disposed within the case;and an insert disposed within the bladder.
 18. The apparatus of claim17, wherein an interior of the bladder is in fluid communication with anambient environment of the apparatus.
 19. The apparatus of claim 17,further comprising a puncture in the bladder.
 20. The apparatus of claim17, further comprising a hole in the case proximate the puncture. 21.The apparatus of claim 17, wherein the bladder comprises a PVC material.22. The apparatus of claim 17, wherein the collapsible insert comprisesan open cell foam material.
 23. The apparatus of claim 17 wherein thebladder forms a space devoid of encapsulant.
 24. The apparatus of claim23, wherein the space is a fixed volume.
 25. The apparatus of claim 24,wherein the insert defines the space.
 26. A kit for encapsulating acomponent within a case, the kit comprising: a bladder shaped to fitwithin a case proximate a component; an insert disposed within thebladder; and encapsulant for at least partially filling the interior ofthe case to be in contact with the component and the bladder.
 27. Thekit of claim 26, wherein the bladder comprises a PVC material.
 28. Thekit of claim 26, wherein the insert comprises an open cell foammaterial.
 29. The kit of claim 26, further comprising an adhesive forattaching the bladder to a wall of the case.
 30. An apparatuscomprising: a case; an electrical component disposed within the case;encapsulate disposed within the case and in contact with at least onesurface of the electrical component; an insert defining a space devoidof encapsulant disposed within the case.
 31. The apparatus of claim 30,wherein the insert comprises an open cell foam material.
 32. Theapparatus of claim 31, further comprising a layer of material imperviousto the encapsulant disposed between the encapsulant and the open cellfoam material.
 33. The apparatus of claim 30, wherein the insertcomprises a bladder containing an open cell foam material and having avent connection.
 34. An apparatus comprising: a case; an electricalcomponent disposed within the case; encapsulate disposed within the caseto a level covering the electrical component; a bladder having a firstportion disposed within the case and a chimney portion extending abovethe level of the encapsulant; and an insert disposed in the bladder. 35.The apparatus of claim 34, wherein the insert is an open cell foammaterial extends from the first portion through the bend to a chimneyportion.
 36. An engine controller for a marine propulsion apparatuscomprising: a case; a circuit board attached to the case at apredetermined height above a bottom of the case; encapsulate disposedwithin the case to a level covering the circuit board; and a bladderdisposed between the bottom of the case and the circuit board anddefining a space devoid of encapsulant, the bladder containing aninsert.
 37. The engine controller of claim 36, wherein the insertcomprises an open cell foam material.
 38. The engine controller of claim37, further comprising: a bend formed in the bladder to define an end ofa chimney portion; and wherein the open cell foam material extendingthrough the bend.
 39. A method of manufacturing an electrical component,the method comprising the steps of: providing a case; positioning abladder containing an insert proximate a bottom of the case, the bladderhaving a chimney portion extending upward away from the bottom of thecase; mounting a circuit board within the case above the bladder, a topof the chimney portion extending above a top of the circuit board;filling the case with encapsulant to a level above the top of thecircuit board but below the top of the chimney portion, the bladderdefining a space devoid of encapsulant between the bottom of the caseand the circuit board.
 40. The method of claim 39, further comprisingthe step of removing a portion of the top of the chimney portion toprovide a vent connection to an interior of the bladder prior to thestep of filling the case with encapsulant.
 41. The method of claim 39,further comprising forming the bladder containing an insert by the stepsof: providing an open cell foam material; covering the open cell foammaterial with a top layer of PVC material and a bottom layer of PVCmaterial; and sealing respective mating sides of the top layer and thebottom layer of PVC material together around a perimeter of the opencell foam material.
 42. The method of claim 39, further comprising thesteps of: positioning the insert to extend into the chimney portion;forming a bend in the bladder to extend the chimney portion upward awayfrom the bottom of the case, the insert extending through the bend;heating the case, bladder and circuit board to remove moisture prior tothe step of filing the case with encapsulant.
 43. A method ofmanufacturing an electrical apparatus, the method of comprising thesteps of: providing a case; installing an electrical component withinthe case; installing an insert and an electrical component within thecase; and introducing encapsulant into the case to cover at least onesurface of the electrical component, wherein the insert defining a spacedevoid of encapsulant within the case.
 44. The method of claim 43,further comprising forming the collapsible insert from an open cell foammaterial.
 45. The method of claim 44, further comprising the step ofcovering at least a portion of the open cell foam material with a layerof material impervious to the encapsulant prior to the step ofintroducing encapsulant.
 46. The method of claim 43, further comprisingthe steps of: forming a bladder around the insert prior to the step ofinstalling the insert.
 47. The method of claim 46, further comprisingthe step of forming a vent opening in the bladder.
 48. The method ofclaim 47, further comprising the step of forming a bend in the bladderto position the vent opening above a top level of the encapsulant priorto the step of introducing encapsulant.